Wireless UEs in communication with a wireless network may be carried on vehicles that travel at high speeds, which may be greater than, for example, 160 km/hr. Such vehicles may include terrestrial or surface vehicles, such as high speed trains (HSTs), which may travel at speeds of more than 250 km/hr.
In connection with Long Term Evolution (LTE) Radio Access Network Working Group 4 (RAN4), a two-path remote radio head (RRH) single-frequency network (SFN) channel model for HST scenarios may enhance network performance for high speed scenarios. A challenge is to accurately estimate the two-path channel impulse response (CIR), which may include tap power, phase, time delay and/or Doppler shift of each path.
In channel estimation, known signals that are sometimes called pilot symbols or pilots may be transmitted along with data to obtain channel knowledge for proper decoding of received signals. Legacy channel estimation may be based on a minimum-mean-square-error (MMSE) linear Wiener filter. In some embodiments, a Doppler spread estimator may only estimate a maximum Doppler shift by using statistical methods. With Doppler spread modeled as a Jakes spectrum, for example, the estimator may employ curve fitting for a Bessel function. Such channel estimation may be suited to providing estimation of multipath fading channels, where there may be an arbitrary number of different paths in which each path may be characterized by an independently random Doppler shift with a probability density function (p.d.f.) distribution proportional to a Doppler power spectrum. However, such channel estimation may be inaccurate for high speed, two-path RRH SFN scenarios, which may arise in connection with HSTs.